The present invention relates generally to an apparatus and a process for supplying a chemical to processing units for producing semiconductor devices, and, more particularly to a process and apparatus for supplying a chemical prepared by diluting and mixing stock solutions to semiconductor production-processing units.
Various types of chemical supplying apparatus are employed in the production of semiconductor devices. The chemicals supplying apparatus supply chemicals, prepared by diluting stock solutions with pure water or by mixing a plurality of stock solutions, to processing units which are used to fabricate semiconductor devices. If a chemical supplied to the processing units is unstable due to changes in its composition, aggregation of finely divided particles contained in the chemicals, etc., the semiconductor devices will be defective. Accordingly, chemicals supplying apparatus which supply stable chemicals are required.
Conventional chemical supplying apparatus, for example, a slurry feeder which supplies a slurry to a chemical machine-polishing unit (hereinafter simply referred to as CMP unit) includes a first tank in which stock solutions are diluted and mixed to prepare the slurry and a second tank in which the slurry is stored. The slurry feeder first draws stock solution (e.g., a suspension of alumina serving as abrasive grains and a solution of ferric nitrate serving as an oxidizing agent) from stock solution tanks and supplies the stock solutions to the first tank. The slurry feeder also supplies pure water to the first tank to carry out diluting and mixing treatment, thereby forming a slurry having a predetermined concentration. The slurry feeder then feeds the slurry to the second tank to store the slurry therein. The slurry feeder supplies the slurry to CMP units employing various kinds of pumps based on commands from the CMP units during polishing treatment. When the amount of slurry in the second tank decreases to a preset level, the slurry feeder prepares a new batch of slurry to supplement the slurry in the second tank, ensuring storage of a sufficient amount of slurry in the second tank.
Slurries tend to aggregate when dried or stored at sites where they dwell. Accordingly, aggregation of a slurry in a passage through which the slurry flows prevents the slurry feeder from supplying the slurry. Unfortunately apparatuses for feeding only general fluids, which do not have mechanisms for flushing passages through which slurries flow, have conventionally been utilized as slurry feeders. Accordingly, the slurry in the passage or pipe aggregates, causing clogging of the pipe. In addition, agglomerates of abrasive grains can be supplied to CMP units and form scratches on the surfaces of wafers undergoing polishing treatment, leading to low wafer yield.
Further, in slurries, particularly metal slurries prepared by mixing and diluting a suspension of alumina serving as abrasive grains and a solution of ferric nitrate serving as an oxidizing agent, precipitation occurs relatively quickly. Thus, polishing rates (speed etc.) decrease over time. Such reduction in the polishing rates means that the thus formed slurry has a predetermined tank life. However, in the system where slurries are continuously stored in the second tank, former batches of slurries remain in the tank, which causes variations in the wafer polishing period, making it impossible to achieve high-accuracy polishing of wafers.
In the apparatus for supplying a chemical, since the chemical stored in the second tank evaporates, which changes concentrations of the components in the second tank, it is not preferred to store the chemical in the second tank over a long period. Accordingly, chemicals not used over long periods are frequently discarded, leading to waste of chemicals and stock solutions.
It is an objective of the present invention to provide an apparatus for supplying a chemical which can supply new batches of chemical solution stably.
To achieve the above objective, the present invention provides a chemical supply apparatus for preparing a mixture by mixing a plurality of stock chemicals and supplying the mixture to at least one processing unit, the apparatus comprising: a plurality of mixing tanks, each mixing tank having a capacity corresponding to an amount of the mixture required by the processing unit, the mixing tanks for preparing the mixture by mixing predetermined amounts of the stock chemicals; a main circulating pipe commonly connected to the plurality of mixing tanks and the processing unit for supplying the mixture in the mixing tanks to the processing unit; a plurality of circulating pipes connected to each of the mixing tanks, respectively, to circulate the mixture in each one of the mixing tanks; a plurality of liquid level sensors for respectively measuring the amount of liquid disposed in each of the mixing tanks; a plurality of selector valves respectively connected between each of the mixing tanks, the circulating pipes, and the main circulating pipe, for selectively connecting the mixing tanks to one of the main circulating pipe and its respective circulating pipe; and a control unit for controlling the selector valves based on the detected liquid levels in the mixing tanks such that one of the plurality of mixing tanks is connected to the main circulating pipe and the other mixing tanks are connected to their respective circulating pipes, wherein a new mixture is prepared in the other mixing tanks while the one mixing tank is supplying its mixture to the processing unit and when the liquid level of the mixture in the one tank reaches a first predetermined low level, the control unit switches the selector valves such that one of the other mixing tanks supplies its mixture to the processing unit.
The present invention further provides a chemical supply apparatus for preparing a mixture by mixing a plurality of stock chemicals and supplying the mixture to at least one processing unit, the apparatus comprising: a first mixing tank and a second mixing tank, each having a capacity corresponding to an amount of the mixture required by the processing unit, each mixing tank for preparing a batch of the mixture by mixing predetermined amounts of the stock chemicals and water; a main circulating pipe commonly connected to the each of the first and second mixing tanks and the processing unit for supplying the mixture in the mixing tanks to the processing unit; a first circulating pipe and a second circulating pipe connected to the first and second mixing tanks, respectively, to circulate the mixture in each one of the mixing tanks; a liquid level sensor provided with each of the mixing tanks for respectively measuring the amount of liquid disposed in each of the mixing tanks; first and second selector valves respectively connected between each of the mixing tanks, the circulating pipes, and the main circulating pipe, for selectively connecting the mixing tanks to one of the main circulating pipe and its respective circulating pipe; and a control unit for controlling the selector valves based on the detected liquid levels in the mixing tanks, the control unit connecting one of the mixing tanks to the main circulating pipe and the other mixing tank to its circulating pipe, wherein when the liquid level of the mixture in the one tank reaches a first predetermined low level, the control unit begins to prepare a new batch of the mixture in the other mixing tank.
The present invention further provides a chemical supply apparatus for preparing a mixture by mixing a plurality of stock chemicals and supplying the mixture to at least one processing unit, the apparatus comprising: a plurality of stock chemical tanks for respectively storing the stock chemicals; a plurality of circulating tanks corresponding to the stock chemical tanks for circulating the stock chemicals, respectively; a feeding system for feeding predetermined amounts of the stock chemicals to the circulating tanks; a plurality of circulating pipes respectively connected to the circulating tanks, to circulate the mixture in each one of the circulating tanks under a predetermined liquid pressure; a circulating system for circulating the stock chemicals fed to the circulating tanks by way of the circulating pipes; and a plurality of nozzles respectively connected to the circulating pipes to spray the mixture into the processing unit, the nozzle preparing the mixture by mixing the stock chemicals therein immediately before the mixture is sprayed.
The present invention provides a method for preparing a mixture in a first mixing tank and a second mixing tank and supplying the mixture to a processing unit, the method comprising the steps of: mixing a plurality of stock chemicals to prepare the mixture in the first mixing tank; supplying the mixture to the processing unit; starting preparation of a new batch of the mixture in the second mixing tank when the liquid level of the mixture in the first mixing tank drops to a predetermined value; and supplying the mixture prepared in the second mixing tank to the processing unit when the liquid level of the mixture in the first mixing tank drops to a second predetermined value.